An Ancient Greek philosopher from Athens (c. 470–399 BC). He taught the concept of "knowing that you know nothing" and pursued truth through the "Socratic method," a form of cooperative argumentative dialogue to stimulate critical thinking and to draw out ideas and underlying presuppositions. He left no writings of his own; his thoughts were preserved for posterity through the dialogues of his student, Plato. He was eventually accused of corrupting the youth and other crimes, and he died by drinking hemlock, remaining true to his philosophical convictions until the end.

An Ancient Greek philosopher (384–322 BC). A student of Plato and later the tutor to Alexander the Great. Known as the "Father of Western Philosophy" (alongside Plato), he systematized logic and explored every field of knowledge, including metaphysics, ethics, politics, and biology. He emphasized empirical experience and took a demonstrative approach, seeking the essence of things within the realities of the physical world.

A French philosopher and mathematician (1596–1650) regarded as the father of modern philosophy. Through "methodological skepticism," where he rejected all things that could be doubted, he arrived at the fundamental truth: "I think, therefore I am" (Cogito, ergo sum). He advocated for dualism, separating the mind from the body, and had a decisive influence on the modernization of philosophy and science. In mathematics, he invented the Cartesian coordinate system.

The greatest philosopher of modern Germany (1724–1804). He synthesized empiricism and rationalism, establishing "critical philosophy" to critically examine the limits of human cognitive ability. In ethics, he taught the "categorical imperative"—a moral duty that must be followed unconditionally regardless of personal gain—which has had a profound impact on modern ethics and theories of international peace.

A 19th-century German philosopher (1844–1900) who criticized traditional morality and Christianity, famously declaring that "God is dead." He advocated for the "Übermensch" (Overman) who breaks through existing values, the "Amor Fati" (love of fate) which affirms even the harshest destiny, and the "Eternal Recurrence," the idea that history repeats itself infinitely. His work has deeply influenced modern thought and literature.

An Ancient Greek philosopher (c. 427–347 BC). A student of Socrates, he preserved his teacher's thoughts for future generations through numerous dialogues. He proposed the "Theory of Forms," suggesting that the true reality consists of eternal, unchanging, and ideal "Forms" (or Ideas) existing behind the visible world of phenomena, laying the foundation for Western philosophy. He also founded the Academy in Athens to educate future thinkers.

An English empiricist philosopher and political theorist (1632–1704). He argued that the human mind is a blank slate (tabula rasa) at birth and that all knowledge is derived from sensory experience. In politics, he developed the "Social Contract" theory, advocating for the protection of life, liberty, and property as natural rights, and arguing that the state exists by the consent of the governed. His ideas justified the Glorious Revolution and decisively influenced modern democracy and the American Declaration of Independence.

A 19th-century German thinker, economist, and revolutionary (1818–1883). He authored "Das Kapital," which thoroughly analyzed the structure of capitalism and exposed the mechanisms by which workers are exploited. He viewed history as a history of class struggle and, together with Engels, published "The Communist Manifesto," calling for a revolution by the working class and the advent of a communist society, exerting immense influence on international politics and social movements.

An 18th-century philosopher and thinker from Geneva (1712–1778). He criticized the progress of civilization for creating human inequality and urged a "return to nature." In politics, he proposed the concepts of the "Social Contract" and the "General Will," which allow for individual freedom while following the collective will of the community. His work had a major impact on the French Revolution and modern democratic ideals, and his masterpiece "Emile" laid the groundwork for modern educational theory.

An ancient Chinese thinker and philosopher (551–479 BC). The founder of Confucianism, he opened a private school accessible to anyone regardless of social status. He placed "Xiao" (filial piety), the affection for one's kin, and "Ren" (benevolence), compassion for others, at the root of virtue, advocating for "Rule by Virtue" based on etiquette and morality. His words and deeds were compiled by his disciples into the "Analects," which had a decisive influence on the political, moral, and cultural foundations of East Asia.